Unless another study has been done, or unless you are referring to a different study, I think you might be talking about the study done by Mr. Greg Dossey, in 1988 (later updated in 1992). When I ran an advanced Arrest and Control course for Mr. Dossey's ARCON instructors I was privileged by receiving a copy of the study. A university did not do the study. At the time the study was first compiled, Mr. Dossey was a sergeant at the LAPD and he was also the department's Exercise Physiologist. That was in 1988. In 1992, the study was replicated for reasons of comparison and cross-validation by the Training Review Committee of the LAPD. The study dealt with arrest situations that required an officer to address resistant and/or aggressive subjects. The purpose of the study was to determine how to make law enforcement training more efficient by addressing those cases or those types of cases more officers see more often. From that study, an Arrest and Control training program was developed and that program has gone on to influence many agencies across the globe (as you may well know).

As to the 90% quote:

The study determined that the most common type of resistance/aggression that an officer faces in the field during arrests is the suspect pulling his arm away after the officer has made contact with the arm in order to commence cuffing. Four other categories gained large enough a percentage to be noted. As far as going to the ground, the study only says "62% of all altercations involving resistance and/or aggression ended with the officer and the subject on the ground with the officer applying a joint lock and handcuffing the subject." The surrounding context implies that we are dealing with something akin to how Nikyo ends (for non-law enforcement agents) -- not two folks grappling on the ground fighting between the guard and the mount, etc. As far as two folks going to the ground and fighting it out down there, the stat was only 40% of 10.5% (you all can do the math please) -- a very small figure.

Personally, I do not know of another study and I think Mr. Dossey would have handed me any later relevant information if such a study had been done. However, I could be wrong and/or talking about something completely different.

In my opinion, that stat of 90% came from the Gracie's tagline. I do not think it is actually supported by any kind of legitimate study -- not the kind that Mr. Dossey did at least.